P: (4, 1, 5)
Q: (1, 0, -3)
R: (3, 2, -4)
T, r, p, q = Polygon(P, Q, R)
a = Vector(P, Q)
b = Vector(Q, R)
c = Vector(P, R)
γ = Angle(Q, P, R)
β = Angle(P, R, Q)
α = Angle(P, Q, R)